1. Field of the Invention
The present invention relates to an improvement in an automatic control system for construction machines which automatically perform leveling of ground and paving. The construction machines are used in the civil engineering and construction field and include, for example, motor graders, pavers, and bulldozers.
2. Description of the Related At
In the civil engineering and construction field, the ground leveling implements of a construction machine, such as a blade and a screed, are automatically controlled in performing ground leveling and paving.
In the system for automatically controlling a ground leveling implement that is used in a construction machine, a ground leveling string corresponding to a finished cross section is stretched over the construction site in order to obtain an expected fished surface. The interval between the ground leveling string and the ground leveling implement is detected with a contact type cantilever or a non-contact type ultrasonic sensor. Based on the detection result, the ground leveling implement is controlled so as to follow the ground leveling string. However, the system for automatically controlling a ground leveling implement so that the implement follows a ground leveling string requires a great deal of labor to stretch a ground leveling string over a construction site.
Hence, there has been proposed an automatic control system for construction machinery which is capable of automatically controlling a ground leveling implement and obtaining an expected finished surface without stretching a ground leveling string over a construction site.
An example of the aforementioned automatic control system is shown in FIG. 1. In the figure, reference numeral 1 denotes a bulldozer which is a construction machine for leveling a construction site, 2 a rotating laser unit installed in a construction site, 3 a blade which is a ground leveling implement, 4 a pole attached to the blade 3, and 5 a laser sensor fixed to the pole 4.
The rotating laser unit 2 forms a reference plane Rs at a position of a predetermined height (h) away from a finished plane 6 by means of a generated laser beam. The blade 3 is controlled so that the laser light from the rotating laser unit 2 strikes against the vertical center Ho of the laser sensor 5 (center Ho in the height direction of the laser sensor 5), by an oil pressure control unit 7 serving as ground leveling implement control means. In this way, the ground of a construction side is leveled to an expected finished plane 6. According to this automatic control system for construction machines, a ground leveling operation and a paving operation can be simply performed compared with an operation of stretching a ground leveling string over a construction site.
However, in the case where the ground 6' and finished plane 6 of a construction site have a complicated configuration with undulations and inclination, the rotating laser unit 2 has to be reinstalled as shown in FIG. 2 in order to obtain the reference plane Rs. For this reason, in the case of the leveling and paving of complicated ground contours reinstalling the rotating laser unit 2 will be troublesome.
Hence, another system for automatically controlling the construction machine 1 has been proposed. This system employs an automatic tracking type survey unit (also called a total tracking station), which is available as "AP-L1" manufactured by TOPCON. The automatic tracking type survey unit measures a distance to a target, a horizontal angle between a reference direction and a direction in which the target exists, and a vertical angle between a reference height and a direction in which the target exists, and tracks the target.
FIG. 3 illustrates an example of the system for automatically controlling a construction machine by employing an automatic tracking type survey unit. In the figure, reference numeral 8 denotes an automatic tracking type survey unit, which is installed at the known coordinate point O of a construction block. The survey unit 8 is connected to a personal computer (PC) 9, which is in turn connected to a radio transmitter 10. A bulldozer 1 is provided with a blade 3, a pole 4 attached to the blade 3, an oil pressure control unit 7, a prism 11 attached to the pole 4 as a target to be tracked, and a radio receiver 12.
The PC 9 stores finished-height data that defines the desired elevation of the finished ground surface at each coordinate position. The height of the finished surface is usually expressed by an elevation or height relative to a known reference such as sea level. The survey unit 8 tracks the prism 11 with a tracking light L and measures the distance from the known coordinate position O to the prism 11 and the horizontal angle between a reference direction and a direction in which the prism 11 exists. Based on the measured distance and horizontal angle, the survey unit 8 computes at least the horizontal coordinate position of the prism 11 (target) relative to the known coordinate O. The computed horizontal coordinate position data is transferred from the survey unit 8 to the PC 9.
The PC 9 calls out finished-height data corresponding to the computed horizontal coordinate position. Then, the PC 9 transfers the finished-height data to the radio transmitter 10. The radio transmitter 10 transmits the finished-height data to the radio receiver 12. The oil pressure control unit 7 controls the blade 3, based on the finished-height data received by the radio receiver 12. The blade 3 digs or cuts ground so that the ground has a designed fished height.
The system for automatically controlling a construction machine with the automatic tracking type survey unit 8 has an advantage that a complicated finished ground surface can be created without increasing the number of steps, because the blade 3 is controlled based on the finished-height data.
Incidentally, the conventional automatic total tracking station 8 is constituted so that it tracks a target in both a horizontal direction and a vertical direction. The automatic total tracking station 8 detects the target position of the target, such as prism 11, through a telescope and feeds back the offset quantity i.e., offset between the target position and the optical axis center of the barrel portion of the telescope to a horizontal-vertical drive servo motor. In this way, the automatic total tracking station 8 is controlled so that the optical axis center tracks the target. However, there is a limit to the response time, and in the case where the vibration cycle of the target is fast, the station 8 cannot follow it and a dead zone will occur. Also, in the conventional tracking control system, the height of the ground leveling implement 3 is controlled based on finished height data, and if the height of the ground leveling implement 3 changes, the tracking light follows this change. Because the tracking light follows the change, there are cases where the tracking station 8 will give rise to a hunting phenomenon. Therefore, when the construction machine 1 travels on a desert road surface, there is the possibility that the vertical vibration, will cause an error in the position detection.
In addition, since the ground leveling implement 3 itself of the construction machine 1 has a specific response speed and is automatically controlled, control is repeated between the construction machine 1 and total tracking station 8. This repetitive control causes a degradation in finished-height precision. Generally, in the case of the construction machine 1 which performs leveling of ground and paving, vertical (height-direction) finishing precision is required. This requirement hinders the use of the automatic total tracking station 8.
Another automatic control system has been proposed in U.S. patent application Ser. No. 08/658655 (filed on Jun. 5, 1996) now U.S. Pat. No. 5,771,978. The automatic total tracking station 8 tracks a target only in a horizontal direction and does not track it in a vertical direction. In this automatic control system, the total tracking station 8 is provided with a fan laser having a horizontal rotation or spread, and the horizontal coordinate position of a target is detected by horizontal tracking. The finished height data at the detected horizontal coordinate position is read out of storage, and the tracking station projects the fan beam to the designed height (finished height) at the detected horizontal coordinate position. The construction machine 1 is provided with a laser sensor, and this sensor detects the fan beam. Based on the difference between the vertical (height-direction) center of the laser sensor and the vertical position at which the fan beam was radiated on the laser sensor, the ground leveling implement is controlled so that the fan beam radiates the center of the laser sensor.
According to the aforementioned structure, one can obtain a finished height with a high degree of accuracy without being influenced by the vibration of the construction machine 1, because vertical tracking is based on finished height data, not the vertical position of a moving target. Also, vertical direction control of the ground leveling implement 3 of the construction machine 1 occurs only if the fan laser light is controlled so that it can be received at the vertical center of the laser sensor, and there is the advantage that control equal to or greater than the conventional control based on a rotating laser can be easily achieved.
However, in the aforementioned control system, for controlling the ground leveling implement 3 of the construction machine 1, an additional fan laser light source must be provided and, therefore, there is a disadvantage that the survey unit 8 becomes complicated structurally. Furthermore, in order to give construction information, such as the inclination of the ground leveling implement 3, to the operator of the construction machine 1, additional communication means for communicating the construction information is required, as with the control system employed in the conventional automatic total tracking station.